October 26, 740 Tsunami: Marmara Sea, Turkey

Name: October 26, 740 Tsunami: Marmara Sea, Turkey
Start: 0740-10-26
Location: Marmara Sea, Turkey

October 26, 740 · Deaths: many · Questionable tsunami

A tsunami caused by a magnitude 7.3 earthquake began at Marmara Sea, Turkey on October 26, 740. Its effects were recorded at 2 places.

Where the waves reached

The source (white) and every runup with a place, colored by the water height recorded there. A ring is a runup NCEI marks doubtful.

Under 1 m
1 to 3 m
3 to 10 m
10 to 30 m
30 m and more
Height not recorded

Tsunami warnings in force

Travel times

How long the first wave took to reach each part of the ocean, one line for each hour up to 24, estimated from the source and the depth of the sea.

The travel times are computed in your browser, which needs JavaScript.

1 to 4 hours
5 to 6 hours
7 to 14 hours
15 hours and more

Computed in your browser the way NOAA’s own travel time maps are: the wave travels at the square root of gravity times the depth, over NOAA’s ETOPO1 depths averaged to a 10 arc-minute grid. Checked against NOAA NCEI’s maps for 21 tsunamis over the first 24 hours, these lines fall within 10 minutes of NCEI’s at half the points compared and within 52 minutes at 9 in 10. They give when the first wave could arrive, not how high it is; bays, harbors and island chains finer than the grid can see it later. Not for use in a warning: see tsunami.gov.

The tsunami

Date: October 26, 740
Source: Marmara Sea, Turkey
Cause: Earthquake
Earthquake: Magnitude 7.3
Runups recorded: 2
Tsunami intensity (Soloviev-Imamura): 3
Waters: Ocean
How certain: Questionable tsunami
Source location: 40.700° N, 29.300° E

The toll

Deaths: Many (about 101 to 1,000) with the earthquake or eruption that caused it
Damage: Severe (about $5 to $25 million) with the earthquake or eruption that caused it
Houses destroyed: Many (101 to 1,000) with the earthquake or eruption that caused it

Where the literature gives no number, NCEI records a description on a scale of 1 to 4, printed here in its words. Damage is in millions of US dollars of the year of the event, not adjusted for inflation.

What the record says

NCEI’s account, from the sources it cites.

740, October 26. 40o42'N, 29o18'E, magnitude 7.3. A period of seismic activity lasting for almost one year (or two) in the area of Costantinople. On October 26 a disastrous earthquake caused serious damage in Costantinople, in the villages of Thrace and in Bytinia. Many people killed. Nicea (today Iznik) and Nicomedia (today Izmit) affected. Sea withdrawal, followed by inundation of many towns (Theophanes, ref #10486; Monaco,ref #10490). (reference #4139)

740, October 26, 08h. Zone of the Sea of Marmara. A strong earthquake occurred in Thrace and in Constantinople that destroyed many houses, temples, monasteries. Inland fortifications collapsed; statues fell down from public buildings. A great number of people were killed. The earthquake was also destructive in Izmit. Underground shocks lasted 11 months. months. The sea receded from the coast in many places, soon came back and flooded cities; i = 3 on the Thracian coast of the Sea of Marmara and in Izmit. (reference # 2130).

740 October 26. Sea of Marmara, Izmit, Ienik Lake, Thracian coasts of Marmara (iii). (reference #15)

740 October 26. Turkey, Thrace, and Constantinople. Sea retired, then returned. (reference #132)

740, October 26. Marmara Sea, 41oN, 28o42'E, intensity IX, magnitude 7.4. (reference #330)

740 AD. October 26. Sea of Marmara, Izmit, Zznik Lake, Thracian Coasts of Marinara (iii). Fourteen years after the eruption of the volcano of Thera a disastrous earthquake occurred in Constantinople. The walls and many public buildings collapsed and over one thousand people perished. Many towns in Thrace were also destroyed among which Nicea (Iznik), Nicomedia (Izmit) and Praenetos. The sea retired in many places and returning soon after inundated many towns. The date of this event is 26 October 740 AD, to which all writers concerned agree. No description of the seismic sea-wave was found. (reference #24)

Every runup

Nearest the source first. Heights are above sea level at the time; a tide gauge reads half the wave’s full height.

Where	Country	Km from source	Water height, m	Inland, m	Measured by	First wave, UTC	Deaths
Thracian Coast	Turkey	42			Eyewitness observation of water height
Izmit	Turkey	55			Eyewitness observation of water height

Every tsunami in 740 The 700s Tsunamis of Turkey The earthquake This day in weather history Alerts in force

Sources

Tsunami events and runups from NOAA’s National Centers for Environmental Information, Global Historical Hazard Database, cited as NCEI/WDS, doi:10.7289/V5PN93H7. Public domain. Read 2026-09-24. NCEI tsunami event 56.